

You’re opening a port in your VPN connection so no there’s no “huge vulnerability” (even without a VPN you’re only opening a port to your torrent client) and as mentioned, you’re only seeding to people who have port forwarding set up. If more people run without it like yourself, the whole system breaks down.
I don’t know if this will be of any help, and I dont fully understand the intricacies, but I run into similar issues with my HomeAssistant setup when the certificates expire (every couple of months?). The issue is that HA doesn’t pull the new certificate without a reboot, so I typically just restart it every once in a while to ensure that it has the newest certificate.